Fluororubbers are excellent in fuel barrier properties, slidability, heat resistance, chemical resistance, weather resistance, electric insulation properties, etc. and are used in a wide range of fields including automobiles, industrial machines, OA equipments, electric and electronic equipments, etc.
In the automobile industry, as environmental regulations in recent years, SHED (Sealed Housing for Evaporative Determination) regulations have been strengthened, which prescribe rules on the fuel evaporation gas amount that is released from cars using gasoline as fuel.
As a fuel for automobiles, gasoline, LPG, light oil or an alcohol-containing fuel may, for example, be mentioned. An alcohol-containing fuel is a fuel obtained by mixing gasoline and an alcohol, and since it contains oxygen, it has environmental improvement potentials (characteristics as a low-pollution fuel) such that emission of carbon monoxide or soot (black smoke) is low, emission of SOx or NOx is low, and photochemical reactivity is low. Therefore, it is expected to use an alcohol-containing fuel as the fuel for automobiles, and development of a rubber material having barrier properties against an alcohol-containing fuel is desired.
A tetrafluoroethylene/perfluoro(alkyl vinyl ether)-type elastomer is called a perfluoroelastomer (hereinafter referred to also as FFKM), and its cross-linked cured product is known to be excellent in chemical resistance.
Non-Patent Document 1 discloses that a cross-linked cured product of FFKM shows little volume increase (swelling) by the immersion test and thus has good resistance against each of gasoline and methanol (Non-Patent Document 1, page 630, Table III. 3.4). Therefore, the cross-linked cured product of FFKM is considered to have barrier properties against an alcohol-containing fuel.
However, FFKM has a disadvantage that it is expensive, and while it has excellent characteristics, its applications are rather limited at present.
Patent Document 1 discloses that when FFKM and a tetrafluoroethylene (hereinafter referred to also as TFE)/propylene (hereinafter referred to also as P) elastomer are used as a mixed, heat resistance is improved as compared with the case of using FFKM alone. As examples of the TFE/P elastomer, in addition to the binary elastomer of TFE/P, 7 types of ternary elastomer are mentioned. As one example of the ternary elastomer, an elastomer of TFE/P/vinylidene fluoride (hereinafter referred to also as VdF) in a molar ratio of 40-60/60-40/1-10 is disclosed.